donot interfere with the analytical procedure. This can be evaluated by analyzingthe filtered dissolution medium and comparing it with the unfiltered medium.
过滤时可能会发生药物的吸附，需要进行评估。过滤材料将与溶出介质相互作用，影响每个溶质的回收率应该根据具体问题进行考虑。不同的过滤材料表现出与药物结合的不同特性。由于药物与滤膜结合引起药物从滤液中损失的比例，可能依赖于药物浓度。因此，应采用预期浓度范围内不同浓度的样品溶液来评估滤膜吸附干扰。由于药物吸附是可饱和的，弃去一定体积的初滤液，收集续滤液，以达到接近原来的溶液浓度的样品也是可取的。通常选择适合的过滤材料，最大限度地减少滤膜吸附干扰，润湿滤膜对减少吸附也是必要的。此外，过滤后的溶出物不干扰分析检测也是非常重要的，这可以通过过滤后的溶出介质过滤与未过滤的溶出介质进行比较，评估滤膜是否干扰分析测定。
The filter size should be based on thevolume to be withdrawn and the amount of particles to be separated. Use of thecorrect filter dimensions will improve throughput and recovery, and also reduceclogging. Use of a large filter for small-volume filtration can lead to loss ofsample through hold-up volume, whereas filtration through small filter sizesneeds higher pressures and longer times, and the filters can clog quickly.
根据要过滤样品溶液的体积以及样品溶液中颗粒的量选择滤膜孔径。使用正确的滤膜孔径将提高溶液的通过率和回收率，并减少滤膜堵塞。使用大孔径滤膜过滤小体积溶液，能够导致样品溶液损失量过大而收集不到所用样品量；使用小孔径滤膜过滤，需要更高的压力和较长的时间，并且溶液迅速堵塞滤膜。 Filters used for USP Apparatus 4 needspecial attention because they are integrated in the flow-through process.Undissolved particles may deposit on the filters, creating resistance to theflow.
USP仪器4中使用的过滤器需要特别注意，因为它们在流动过程中使用。不溶颗粒会沉积在过滤器，产生流动阻力。
In the case of automated systems,selection of the filter with regard to material and pore size can be done in asimilar manner to manual filtration. Flow rate through the filter and cloggingmay be critical for filters used in automated systems. Experimental
verification that a filter isappropriate may be accomplished by comparing the responses for filtered andunfiltered standard and sample solutions. This is done by first preparing asuitable standard solution and a sample solution. For example, prepare atypical dissolution sample in a beaker and stir vigorously with a magneticstirrer to dissolve the drug load completely.For standard solutions, comparethe results for filtered solutions (after discarding the appropriate volume) tothose for the unfiltered solutions. For sample solutions, compare the resultsfor filtered solutions (after discarding the appropriate volume) to those forcentrifuged, unfiltered solutions.
在自动化系统的情况下，关于过滤器滤膜材料和孔径大小可以用类似的方式通过手动过滤进行选择。在自动化系统中通过过滤器的流量和过滤器的堵塞可能是至关重要的。通过试验比较过滤和未过滤的标准溶液和样品溶液的含量差别，验证该过滤器是合适的。首先制备一个合适的标准溶液和样品溶液。例如，在烧杯中制备一个标准溶解样品，用磁力搅拌器搅拌使药物完全溶解。对于标准溶液，比较过滤溶液（弃去的适当体积后）和未过滤溶液的含量测定结果；对于样品溶液，比较过滤（弃去适当体积后）、离心、未过滤样品溶液的含量测定结果。 1.2 Determining Solubility and Stability of DrugSubstance in Various Media 1.2原料药在不同溶出介质中的溶解度测定和稳定性研究
Physical and chemical characteristics of the drug substance need to be determinedas part of the process of selecting the proper dissolution medium. Whendeciding the composition of the medium for dissolution testing, it is importantto evaluate the influence of buffers, pH, and if needed, different surfactantson the solubility and stability of the drug substance. Solubility of the drugsubstance is usually evaluated by determining the saturation concentration ofthe drug in different media at 37° using the shake-flask solubility method(equilibrium solubility). To level out potential ion effects between the drugand the buffers used in the media, mixtures of hydrochloric acid and sodiumhydroxide are used to perform solubility investigations; this is in addition tothe typical buffer solutions. In certain cases, it may be necessary to evaluatethe solubility of the drug at temperatures other than 37° (i.e., 25°). The pHof the clear supernatant should be checked to determine whether the pH changesduring the solubility test. Alternative approaches for solubility determinationmay also be used.
在选择合适溶出介质的过程中，需要确定原料药的物理化学特性。当需要确定溶出度试验中溶出介质的组成时，有必要评估缓冲液、pH值、以及不同的表面活性剂（如果需要）对药物的溶解度和稳定性的影响。在37℃温度条件下，采用摇瓶溶解法（平衡溶解度）测定原料药在不同介质中的饱和浓度，来评估药物的溶解性。为了消除溶出介质中药物和缓冲液之间离子的潜在影响，使用盐酸和氢氧化钠的混合物对溶解度进行研究，这是一种典型的缓冲溶液。在某些情况下，评估药物在37℃以外条件下（即，25℃）的溶解度可能也是必要的。在溶解度试验过程中应检查上清溶液的pH值，以确定在溶解过程中pH值是否改变。也可使用其他可供选择的方法进行溶解度测定。
Typical media for dissolution mayinclude the following (not listed in order of preference): diluted hydrochloricacid, buffers (phosphate or acetate) in the physiologic pH range of 1.2–7.5, simulatedgastric or intestinal fluid (with or without enzymes),and water. For somedrugs, incompatibility of the drug with certain buffers or salts may influencethe choice of buffer. The molarity of the buffers and acids used can influencethe solubilizing effect, and this factor may be evaluated.
溶出的典型介质包括（未按照优先顺序列出）：稀盐酸、在生理pH值范围为1.2-7.5缓冲溶液（磷酸盐或者醋酸盐）、模拟胃液或肠液（含有或不含有酶）和水。对于一些药物，与药物不相容的特定缓冲液或盐可能会影响缓冲剂的选择。所使用的缓冲液和酸的体积摩尔浓度能够改变药物的增溶作用，这个因素也需要评估。
Aqueous solutions (acidic or buffersolutions) may contain a percentage of a surfactant [e.g., sodium dodecylsulfate (SDS),polysorbate, or lauryldimethylamine oxide] to enhance thesolubility of the drug. The surfactants selected for the solubilityinvestigations should cover all common surfactant types, i.e.,
anionic,nonionic, and cationic. When a suitable surfactant has been identified,different concentrations of that surfactant should be investigated to identifythe lowest concentration needed
to achieve sink conditions. Typically,the surfactant concentration is above its critical micellar concentration(CMC). Table 1 shows a list of some of the surfactants used indissolution media. Approximate CMC values are provided with
referenceswhenavailable. The list is not comprehensive and is not intended to exclude surfactantsthat are not listed. Other substances, such ashydroxypropyl b
-cyclodextrin,have been used as dissolution media additives to enhance dissolution of poorlysoluble compounds.The U.S. Food and Drug Administration (FDA) maintains adatabase of dissolution methods, including information on dissolution mediathat have been used (1). Typically, the amount of surfactant added issufficient to achieve sink conditions in the desired volume of dissolutionmedium.
有时候水溶性介质中（酸性水溶液或缓冲溶液）可能添加一定比例的表面活性剂（如十二烷基硫酸钠（SDS），聚山梨醇酯，或十二烷基二甲基氧化胺）以提高药物的溶解度。选择用于溶解度研究的表面活性剂时应涵盖所有常用种类的表面活性剂，比如阴离子、非离子型和阳离子，当已经确定一个合适的表面活性剂时，应对表面活性剂的不同浓度进行研究，以确定达到漏槽条件所需的最低浓度。一般情况下，表面活性剂的浓度高于它的临界胶束浓度（CMC）。表1列出了溶出介质中常用的表面活性剂，表中提供了CMC的近似临界值，以便我们参考，此外，表中所列表面活性剂并不全面，不能排除未列出的表面活性剂。其他表面活性剂，如羟丙基β-环糊精，已被用来作为溶出介质添加剂提高难溶性化合物的溶解度，美国食品药品管理局（FDA）溶出度数据库中，已经收载含有羟丙基β-环糊精的溶出介质（1）。通常情况下，表面活性剂的加入量以满足达到漏槽条件所需的溶出介质体积。
It is important to control thegrade and purity of surfactants because use of different grades could affectthe solubility of the drug. For example, SDS is available in both a technicalgrade and a high-purity grade. Obtaining polysorbate 80 from different
sourcescan affect its suitability when performing high-performance liquidchromatography (HPLC) analysis.
由于使用不同级别的表面活性剂会影响药物的溶解度，因此要控制表面活性剂的级别和纯度。例如，SDS只有在工业级和高纯度级才可以使用。在使用HPLC方法进行分析时，不同来源的聚山梨酯（吐温）80会影响它的适用性。 There may be effects of counter-ions orpH on the solubility or solution stability of the surfactant solutions. Forexample, a precipitate forms when the potassium salt for the phosphate bufferis used at a concentration of 0.5 M in combination with SDS. This can beavoided by using the sodium phosphate salt when preparing media with SDS.
反离子或pH值可能会影响表面活性剂溶液的溶解性或稳定性。例如，当含有SDS的磷酸盐缓冲液中钾盐浓度为0.5mol/L时，就形成了沉淀析出，但是使用磷酸钠制备含有SDS的介质时，可以避免这种现象发生。
Table 1. Commonly Used Surfactants with Critical Micelle Concentrations
表1 常见表面活性剂的临界胶束浓度
Routinely, the dissolution medium is buffered; however, the useof purified water as the dissolution medium is suitable for products with adissolution behavior independent of the pH of the medium. There are severalreasons why purified water may not be preferred. The water quality can varydepending on its source, and the pH of the water is not as strictly controlledas the pH of buffer solutions. Additionally, the pH can vary from day to dayand can also change during the run, depending on the drug substance andexcipients. Use of an aqueous–organic solvent mixture as a dissolution mediumis discouraged; however,with proper justification this type of medium may beacceptable.
通常，溶出介质为缓冲盐溶液，但是，对于非pH值依赖性的制剂可以使用纯化水作为溶出介质。不推荐使用纯化水作为溶出介质的原因：水的质量变化取决于它的来源，而水的pH值不像缓冲溶液能够严格控制；此外，若药物和辅料的溶出对pH值敏感时需要考虑使用缓冲液。另外使用水-有机溶剂混合物作为溶出介质也是不推荐的，但是，特殊情况下（有充分适当的理由），也是可以接受的。
Investigations of the stability of thedrug substance should be carried out, when needed, in the selected dissolutionmedium with excipients present, at 37°. This elevated temperature has thepotential to decrease solution stability (degradation). Stability should allowfor sufficient time to complete or repeat the analytical procedure. Physicalstability may be of concern when precipitation occurs because of lowersolubility at room or refrigerated temperature.
必要时，应该对原料药的稳定性进行考察，在所选择的溶出介质中加入辅料，在37℃条件下进行考察。这种升高的温度会潜在的降低溶液的稳定性（降解）。稳定性试验应考虑到有足够的时间来完成或重复分析过程。当因室温或冷藏贮存时降低药物的溶解度而发生沉淀时，物理稳定性也需要关注。 1.3 Choosing aMedium and Volume 1.3溶出介质和体积的选择
When developing a dissolution procedure, one goal is to have sinkconditions, which are defined as having a volume of medium at least three timesthe volume required to form a saturated solution of drug substance. When sinkconditions are present, it is more likely that dissolution results will reflectthe properties of the dosage form. A medium that fails to provide sinkconditions may be acceptable if it is appropriately justified. The compositionand volume of dissolution medium are guided by the solubility investigations.For example, the choice and concentration of a surfactant need to be justifiedfrom the solubility data and the dissolution profiles.
当开发一个溶出试验方法时，首先要满足漏槽条件，漏槽条件定义为溶出介质体积至少为药物达到饱和溶液所需体积的三倍。当满足漏槽条件后，溶出度结果能够更好的反映药物制剂的质量。在适当条件下，介质不满足漏槽条件也是可以接受的。溶解介质的组成和体积应根据溶解度的试验结果进行调整。例如，表面活性剂种类和浓度选择，需要根据药物溶解度数据和溶出曲线进行调整。 The use of enzymes in the dissolutionmedium is permitted, in accordance with Dissolution <711>, when dissolution failures occur as a result of cross-linkingwith gelatin capsules or gelatin-coated products. A discussion of thephenomenon of crosslinking and method development using enzymes can be found
inCapsules–Dissolution Testing and Related Quality Attributes<1094>. Validation should be performed with the method using enzymesaccording to section 5. Validation.
